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Abstract:

A base station communicating with a user device using multiple antennas in
a system where a subframe is composed of multiple slots each composed of
multiple basic time units is disclosed. The base station includes a first
mapping unit configured to map one or more reference signals used for
demodulation of one or more L1/L2 control channels and one or more data
channels to be transmitted from one or more of the antennas within a
predetermined number of basic time units from the beginning of each
subframe; and a second mapping unit configured to map reference signals
used for demodulation of data channels to be transmitted from other ones
of the antennas to one or more basic time units following the basic time
units to which the reference signals used for demodulation of the L1/L2
control channels and the data channels are mapped.

Claims:

1. A base station including multiple antennas and communicating with a
user device using the multiple antennas in a system where a subframe is
composed of multiple slots each composed of multiple basic time units,
the base station comprising:a first mapping unit configured to map one or
more reference signals used for demodulation of one or more L1/L2 control
channels and one or more data channels to be transmitted from one or more
of the antennas within a predetermined number of basic time units from
the beginning of each subframe; anda second mapping unit configured to
map reference signals used for demodulation of data channels to be
transmitted from other ones of the antennas to one or more basic time
units following the basic time units to which the reference signals used
for demodulation of the L1/L2 control channels and the data channels are
mapped.

2. The base station as claimed in claim 1, wherein the first mapping unit
is configured to map the reference signals used for demodulation of the
L1/L2 control channels and the data channels to be transmitted from two
of the antennas within three basic time units from the beginning of each
subframe.

3. The base station as claimed in claim 1, wherein the second mapping unit
is configured to map the reference signals used for demodulation of the
data channels to be transmitted from the other ones of the antennas to
one or more basic time units near a middle of each slot.

4. The base station as claimed in claim 1, whereinone subcarrier and one
basic time unit constitute one resource element;the first mapping unit is
configured to map the reference signals used for demodulation of the
L1/L2 control channels and the data channels to be transmitted from two
of the antennas to predetermined resource elements within three basic
time units from the beginning of each subframe; andthe second mapping
unit is configured to map the reference signals used for demodulation of
the data channels to be transmitted from the other ones of the antennas
to predetermined resource elements in the one or more basic time units
following the basic time units to which the reference signals used for
demodulation of the L1/L2 control channels and the data channels are
mapped.

5. The base station as claimed in claim 4, whereinthe first mapping unit
is configured to change, at a predetermined interval, the resource
elements to which the reference signals used for demodulation of the
L1/L2 control channels and the data channels are mapped; andthe second
mapping unit is configured to change, at the predetermined interval, the
resource elements to which the reference signals used for demodulation of
the data channels are mapped.

6. The base station as claimed in claim 5, wherein the predetermined
interval is a subframe.

7. The base station as claimed in claim 1, wherein the second mapping unit
is configured to determine, resource block by resource block, whether to
map the reference signals used for demodulation of the data channels to
be transmitted from the other ones of the antennas to the one or more
basic time units following the basic time units to which the reference
signals used for demodulation of the L1/L2 control channels and the data
channels are mapped, according to a number of antennas of the user
device.

Description:

TECHNICAL FIELD

[0001]The present invention generally relates to a mobile communication
system employing orthogonal frequency division multiplexing (OFDM) for
downlink. More particularly, the present invention relates to a base
station in the mobile communication system.

BACKGROUND ART

[0002]A successor communication system to W-CDMA and HSDPA (collectively
called UMTS), i.e., Long Term Evolution (LTE), is currently being
discussed by 3GPP that is a standardization group for UMTS. In LTE,
orthogonal frequency division multiplexing (OFDM) is to be used as a
downlink radio access method and single-carrier frequency division
multiple access (SC-FDMA) is to be used as an uplink radio access method
(see, for example, 3GPP TR 25.814 (V7.0.0), "Physical Layer Aspects for
Evolved UTRA," June 2006).

[0003]In LTE, the maximum transmission rate of 100 Mbps is to be supported
for downlink. Also in LTE, the transmission rate is optimized for
respective users moving at low speed and high speed.

[0004]Meanwhile, MIMO transmission (MIMO multiplexing), where different
signals are transmitted in parallel via transmission paths formed by
multiple inputs (transmitting antennas) and multiple outputs (receiving
antennas), is expected to be an indispensable technology for LTE. MIMO
transmission makes it possible to increase the total transmission rate by
the number of parallel transmission paths even if the frequency band is
unchanged.

[0005]As a radio access method for high-speed transmission at several tens
of Mbps or higher, orthogonal frequency division multiplexing (OFDM) is
suitable. In OFDM, orthogonal subcarriers are densely arranged such that
the spectra of the subcarriers overlap each other to improve frequency
efficiency. In OFDM, a signal is divided and is transmitted via multiple
subcarriers. Compared with a method where a signal is transmitted via one
carrier, in a transmission method using n (n is an integer greater than
0) subcarriers, the symbol length becomes n times greater.

[0006]For example, a transmission method as shown in FIG. 1 has been
proposed. In the exemplary transmission method of FIG. 1, a base station
(eNode B: eNB) equipped with four antennas transmits shared data channels
(SDCH) using the four antennas and transmits L1/L2 control channels using
two of the four antennas. Also, the base station transmits reference
signals (RS) unique to the respective antennas from the corresponding
antennas. A reference signal includes bits that are known to both the
sending end and the receiving end before transmission and may also be
called a known signal, a pilot signal, and a training signal.

[0007]Also, in another proposal, the reference signals corresponding to
four antennas of the base station are mapped to leading OFDM symbols in
each transmission slot as shown in FIG. 2 (see, for example, 3GPP TS
36.211 (V0.3.0), January 2007).

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

[0008]However, the above background art technologies have problems as
described below.

[0009]In a proposal for LTE, L1/L2 control channels are mapped within the
first three symbols (OFDM symbols) in each subframe and are transmitted
using two antennas of a base station. Also in a proposal, a broadcast
channel (BCH), a paging channel (PCH), and a synchronization channel
(SCH) are transmitted using up to two antennas.

[0010]Meanwhile, it is proposed to configure a user device to be able to
receive at least an L1/L2 control channel(s) with one or two antennas.
Accordingly, if reference signals corresponding to respective antennas of
a base station are mapped to leading OFDM symbols, options in a
demodulation process at the user device increase. That is, the user
device has to try three demodulation patterns corresponding to a case
where a signal is transmitted using one antenna, a case where a signal is
transmitted using two antennas, and a case where a signal is transmitted
using four antennas.

[0011]One object of the present invention is to solve or reduce one or
more of the above problems and to provide a base station that makes it
possible to reduce demodulation patterns in a reception process at a user
device.

Means for Solving the Problems

[0012]An aspect of the present invention provides a base station including
multiple antennas and communicating with a user device using the multiple
antennas in a system where a subframe is composed of multiple slots each
composed of multiple basic time units. The base station includes a first
mapping unit configured to map one or more reference signals used for
demodulation of one or more L1/L2 control channels and one or more data
channels to be transmitted from one or more of the antennas within a
predetermined number of basic time units from the beginning of each
subframe; and a second mapping unit configured to map reference signals
used for demodulation of data channels to be transmitted from other ones
of the antennas to one or more basic time units following the basic time
units to which the reference signals used for demodulation of the L1/L2
control channels and the data channels are mapped.

[0013]This configuration makes it possible to reduce options in a
demodulation process at a user device.

ADVANTAGEOUS EFFECT OF THE INVENTION

[0014]An aspect of the present invention provides a base station that
makes it possible to reduce demodulation patterns in a reception process
at a user device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a drawing illustrating a transmission method of L1/L2
control channels and shared data channels in a base station equipped with
four antennas;

[0040]The best mode for carrying out the invention is described based on
the following embodiments with reference to the accompanying drawings.

[0041]Throughout the accompanying drawings, the same reference numbers are
used for parts having the same functions, and overlapping descriptions of
those parts are omitted.

[0042]A radio communication system 1000 including a base station according
to an embodiment of the present invention is described below with
reference to FIG. 3.

[0043]The radio communication system 1000 is based on, for example,
Evolved UTRA and UTRAN (also called Long Term Evolution (LTE) or Super
3G). The radio communication system 1000 includes a base station (eNode
B: eNB) 200 and multiple user devices (user equipment: UE) 100,
(1001, 1002, 1003 . . . 100n) (n is an integer
greater than 0). The base station 200 is connected to an upper node such
as an access gateway 300 and the access gateway 300 is connected to a
core network 400. Although only one antenna is shown in FIG. 3, the base
station 200 includes multiple antennas. The user devices 100, are in a
cell 50 and communicate with the base station 200 according to Evolved
UTRA and UTRAN.

[0044]The user devices 100n (1001, 1002, 1003 . . .
100n) have the same configuration and functions and are hereafter
just called the user devices 100n unless otherwise mentioned.

[0045]In the radio communication system 1000, OFDM is used as the downlink
radio access method and SC-FDMA is used as the uplink radio access
method. In OFDM, as described above, a frequency band is divided into
narrow frequency bands (subcarriers) and data are transmitted on the
subcarriers. In SC-FDMA, a frequency band is divided into frequency bands
and the frequency bands are allocated to different terminals for
transmission in order to reduce interference among the terminals.

[0046]Communication channels used in LTE are described below.

[0047]For downlink, a physical downlink shared channel (PDSCH) shared by
the user devices 100n and an LTE downlink control channel are used.
In downlink, the LTE downlink control channel is used to transmit
information on users to be mapped to the physical downlink shared
channel, transport format information for the physical downlink shared
channel, information on users to be mapped to a physical uplink shared
channel, transport format information for the physical uplink shared
channel, and delivery confirmation information for the physical uplink
shared channel; and the physical downlink shared channel is used to
transmit user data.

[0048]For uplink, the physical uplink shared channel (PUSCH) shared by the
user devices 100n and an LTE uplink control channel are used. There
are two types of uplink control channel: an uplink control channel to be
time-division-multiplexed with the physical uplink shared channel and an
uplink control channel to be frequency-division-multiplexed with the
physical uplink shared channel.

[0049]In uplink, the LTE uplink control channel is used to transmit
downlink channel quality indicators (CQI) used for scheduling, adaptive
modulation and coding (AMC), and transmission power control (TPC) of the
physical downlink shared channel, and delivery confirmation information
(HARQ ACK information) for the physical downlink shared channel; and the
physical uplink shared channel is used to transmit user data.

[0050]Next, the base station 200 according to an embodiment of the present
invention is described with reference to FIG. 4. In this embodiment, it
is assumed that the base station 200 is equipped with four antennas.
However, the present invention may also be applied to a base station
equipped with more than four antennas. Also in this embodiment, it is
assumed that each subframe is composed of multiple slots (e.g., two
slots) and each slot is composed of multiple basic time units (e.g.,
seven basic time units). However, the configuration of a subframe may be
changed as necessary. Further in this embodiment, a section composed of
one subcarrier and one basic time unit is called a resource element.

[0052]An L1/L2 control channel #1, a data channel such as a shared data
channel #1, and a reference signal (RS) #1 to be transmitted from an
antenna #1 are input to and multiplexed by the multiplexing unit
2021. The reference signal #1 is used to demodulate the L1/L2
control channel #1 and the data channel #1. For example, as shown in FIG.
6, the L1/L2 control channel #1 is mapped within a predetermined number
of OFDM symbols from the beginning of each subframe, for example, within
the first three basic time units. In other words, the L1/L2 control
channel #1 is mapped to predetermined resource elements within the first
three rows of resource elements from the beginning of each subframe.

[0053]The reference signal #1 is mapped within a predetermined number of
OFDM symbols from the beginning of each slot, for example, within the
first three basic time units. For example, the reference signal #1 is
mapped to predetermined resource elements in the first row of resource
elements in each slot. The reference signal #1 is also mapped to the
fourth or later OFDM symbol in each slot. For example, the reference
signal #1 is mapped to predetermined resource elements in the fifth row
of resource elements in each slot. To improve the accuracy of channel
estimation at the user devices 100n, the reference signal #1 to be
mapped to the fourth or later OFDM symbol in each slot is preferably
mapped to resource elements near the middle of each slot. For example,
the reference signal #1 is preferably mapped to resource elements in the
fourth or fifth row of resource elements in each slot.

[0054]The data channel #1 is mapped to resource elements other than those
to which the L1/L2 control channel #1 and the reference signal #1 are
mapped.

[0055]The multiplexing unit 2021 maps and multiplexes the L1/L2
control channel #1, the reference signal #1, and the data channel #1 and
inputs the multiplexed signal to the IFFT 2041. The IFFT 2041
inverse-Fourier-transforms the multiplexed signal and modulates the
multiplexed signal by OFDM.

[0057]An L1/L2 control channel #2, a data channel such as a shared data
channel #2, and a reference signal (RS) #2 to be transmitted from an
antenna #2 are input to and multiplexed by the multiplexing unit
2022. The reference signal #2 is used to demodulate the L1/L2
control channel #2 and the data channel #2. For example, as shown in FIG.
6, the L1/L2 control channel #2 is mapped within a predetermined number
of OFDM symbols from the beginning of each subframe, for example, within
the first three basic time units. In other words, the L1/L2 control
channel #2 is mapped to predetermined resource elements within the first
three rows of resource elements from the beginning of each subframe.

[0058]The reference signal #2 is mapped within a predetermined number of
OFDM symbols from the beginning of each slot, for example, within the
first three basic time units. For example, the reference signal #2 is
mapped to predetermined resource elements in the first row of resource
elements in each slot. The reference signal #2 is also mapped to the
fourth or later OFDM symbol in each slot. For example, the reference
signal #2 is mapped to predetermined resource elements in the fifth row
of resource elements in each slot. To improve the accuracy of channel
estimation at the user devices 100n, the reference signal #2 to be
mapped to the fourth or later OFDM symbol in each slot is preferably
mapped to resource elements near the middle of each slot. For example,
the reference signal #2 is preferably mapped to resource elements in the
fourth or fifth row of resource elements in each slot.

[0059]The data channel #2 is mapped to resource elements other than those
to which the L1/L2 control channel #2 and the reference signal #2 are
mapped.

[0060]The multiplexing unit 2022 maps and multiplexes the L1/L2
control channel #2, the reference signal #2, and the data channel #2 and
inputs the multiplexed signal to the IFFT 2042. The IFFT 2042
inverse-Fourier-transforms the multiplexed signal and modulates the
multiplexed signal by OFDM.

[0062]A data channel such as a shared data channel #3 and a reference
signal (RS) #3 to be transmitted from an antenna #3 are input to and
multiplexed by the multiplexing unit 2023. The reference signal #3
is used to demodulate the data channel #3. For example, as shown in FIG.
6, the reference signal #3 is mapped, in each slot, to a basic time unit
following the basic time units to which the L1/L2 control channels #1 and
#2 and the reference signals #1 and #2 are mapped by the multiplexing
units 2021 and 2022. In other words, the reference signal #3 is
mapped to the fourth or later OFDM symbol or basic time unit in each
slot, i.e., in a region other than that where the L1/L2 control channels
are mapped. For example, the reference signal #3 is mapped to
predetermined resource elements in the fourth row of resource elements in
each slot. To improve the accuracy of channel estimation at the user
devices 100n, the reference signal #3 to be mapped to the fourth or
later basic time unit in each slot is preferably mapped to resource
elements near the middle of each slot. For example, the reference signal
#3 is preferably mapped to resource elements in the fourth or fifth row
of resource elements in each slot.

[0063]The data channel #3 is mapped to resource elements other than those
to which the reference signal #3 is mapped.

[0064]The multiplexing unit 2023 maps and multiplexes the reference
signal #3 and the data channel #3 and inputs the multiplexed signal to
the IFFT 2043. The IFFT 2043 inverse-Fourier-transforms the
multiplexed signal and modulates the multiplexed signal by OFDM.

[0066]A data channel such as a shared data channel #4 and a reference
signal (RS) #4 to be transmitted from an antenna #4 are input to and
multiplexed by the multiplexing unit 2024. The reference signal #4
is used to demodulate the data channel #4. For example, as shown in FIG.
6, the reference signal #4 is mapped, in each slot, to a basic time unit
following the basic time units to which the L1/l2 control channels #1 and
#2 and the reference signals #1 and #2 are mapped by the multiplexing
units 2021 and 2022.

[0067]In other words, the reference signal #4 is mapped to the fourth or
later OFDM symbol or basic time unit in each slot, i.e., in a region
other than that where the L1/L2 control channels are mapped. For example,
the reference signal #4 is mapped to predetermined resource elements in
the fourth row of resource elements in each slot. To improve the accuracy
of channel estimation at the user devices 100n, the reference signal
#4 to be mapped to the fourth or later basic time unit in each slot is
preferably mapped to resource elements near the middle of each slot. For
example, the reference signal #4 is preferably mapped to resource
elements in the fourth or fifth row of resource elements in each slot.

[0068]The data channel #4 is mapped to resource elements other than those
to which the reference signal #4 is mapped.

[0069]The multiplexing unit 2024 maps and multiplexes the reference
signal #4 and the data channel #4 and inputs the multiplexed signal to
the IFFT 2044. The IFFT 2044 inverse-Fourier-transforms the
multiplexed signal and modulates the multiplexed signal by OFDM.

[0071]The scheduler 208 performs scheduling of the reference signals #3
and #4 and thereby causes the multiplexing units 2023 and 2024
to map, in each slot, the reference signals #3 and #4 to resource
elements in a region other than that where the L1/L2 control channels are
mapped. For example, the scheduler 208 maps the reference signals #3 and
#4 to the fourth or later OFDM symbol in each slot.

[0072]Each of the multiplexing units 2021, 2022, 2023, and
2024 may be configured to change resource elements to which the
L1/L2 control channel and/or the reference signal is mapped at a
predetermined interval, for example, every subframe. For example, each of
the multiplexing units 2021, 2022, 2023, and 2024 may
be configured to cause the L1/L2 control channel and/or the reference
signal to "hop" from previous resource elements to adjacent resource
elements, i.e., to map the L1/L2 control channel and/or the reference
signal to the adjacent resource elements in the next subframe.

[0073]Also, the multiplexing units 2023 and 2024 may be
configured to determine, resource block by resource block, whether to map
the reference signals #3 and #4 to basic time units following the basic
time units to which the L1/l2 control channels #1 and #2 and the
reference signals #1 and #2 are mapped by the multiplexing units
2021 and 2022 according to the numbers of antennas of the
respective user devices 100n. In the example shown in FIG. 7, the
reference signals #1, #2, #3, and #4 are mapped to resource elements in
resource blocks allocated to a user device #1 equipped with four antennas
and the reference signals #1 and #2 are mapped to resource elements in
resource blocks allocated to a user device #2 equipped with two antennas.

[0074]Next, the user device 100 (generally refers to any one of the user
devices 100n) of this embodiment is described with reference to FIG.
5.

[0078]The CP removing unit 102 removes guard intervals from received
symbols and thereby extracts effective symbols from the received symbols.

[0079]The fast Fourier transform unit (FFT) 104 fast-Fourier-transforms an
input signal and inputs the fast-Fourier-transformed signal to the
switching unit 108 or 120. The FFT 104 inputs an L1/L2 control channel to
the switching unit 108 and inputs a data channel to the switching unit
120.

[0080]The switching unit 108 selects a demodulation process (one-antenna
demodulation process) for a signal transmitted with one antenna or a
demodulation process (two-antenna demodulation process) for a signal
transmitted with two antennas according to the number of antennas (one or
two) used by the base station 200 to transmit the L1/L2 control channel.
For example, the user device 100 reports the number of its antennas to
the base station 200 during a connection process.

[0081]The base station 200 determines the number of antennas used to
transmit the L1/L2 control channel based on the number of antennas
reported by the user device 100. For example, the base station 200 uses
one antenna for transmission if the number of antennas of the user device
100 is one or uses two antennas for transmission if the number of
antennas of the user device 100 is two or more. The switching unit 108
inputs a selection result indicating which one of the one-antenna
demodulation process and the two-antenna demodulation process is selected
to the switching unit 116.

[0082]When the L1/L2 control channel is transmitted using one antenna from
the base station 200, the fast-Fourier-transformed signal is input to the
demultiplexing unit 110 (1). The demultiplexing unit 110 separates the
input signal into a reference signal (RS) #1 and the L1/L2 control
channel, inputs the RS #1 to the channel estimation unit 1121, and
inputs the L1/L2 control channel to the demodulation unit 114. The
channel estimation unit 1121 performs channel estimation based on
the RS#1 and inputs the result of channel estimation to the demodulation
unit 114. The demodulation unit 114 demodulates the L1/L2 control channel
based on the result of channel estimation and inputs the demodulated
L1/L2 control channel to the switching unit 116.

[0083]When the L1/L2 control channel(s) is transmitted using two antennas
from the base station 200, the fast-Fourier-transformed signal is input
to the demultiplexing unit 110 (2). The demultiplexing unit 110 separates
the input signal into a reference signal (RS) #1, a reference signal (RS)
#2, and the L1/L2 control channel(s), inputs the RS #1 and the RS#2 to
the channel estimation units 1121 and 1122, and inputs the
L1/L2 control channel(s) to the demodulation unit 114. The channel
estimation unit 1121 performs channel estimation based on the RS#1
and the channel estimation unit 1122 performs channel estimation
based on the RS#2. The results of channel estimation are input to the
demodulation unit 114. The demodulation unit 114 separates the L1/L2
control channel(s) into L1/L2 control channels transmitted from the
respective antennas, demodulates the L1/L2 control channels based on the
corresponding results of channel estimation, and inputs the demodulated
L1/L2 control channels to the switching unit 116.

[0084]The switching unit 116, according to the selection result input from
the switching unit 108, outputs either the L1/L2 control channel
demodulated by the one-antenna demodulation process or the L1/L2 control
channels of the respective antennas demodulated by the two-antenna
demodulation process.

[0085]The switching unit 120 selects a demodulation process (one-antenna
demodulation process) for a signal transmitted with one antenna, a
demodulation process (two-antenna demodulation process) for a signal
transmitted with two antennas, or a demodulation process (four-antenna
demodulation process) for a signal transmitted with four antennas
according to the number of antennas used by the base station 200 to
transmit a data channel(s). Also, the switching unit 120 inputs a
selection result indicating which one of the one-antenna demodulation
process, the two-antenna demodulation process, or the four-antenna
demodulation process is selected to the switching unit 128.

[0086]When the data channel is transmitted using one antenna from the base
station 200, the fast-Fourier-transformed signal is input to the
demultiplexing unit 122 (1). The demultiplexing unit 122 separates the
input signal into a reference signal (RS) #1 and the data channel, inputs
the RS #1 to the channel estimation unit 1241, and inputs the data
channel to the signal separation/demodulation unit 126. The channel
estimation unit 1241 performs channel estimation based on the RS#1
and inputs the result of channel estimation to the signal
separation/demodulation unit 126. The signal separation/demodulation unit
126 demodulates the data channel based on the result of channel
estimation and inputs the demodulated data channel to the switching unit
128.

[0087]When the data channel(s) is transmitted using two antennas from the
base station 200, the fast-Fourier-transformed signal is input to the
demultiplexing unit 122 (2). The demultiplexing unit 122 separates the
input signal into a reference signal (RS) #1, a reference signal (RS) #2,
and the data channel(s), inputs the RS #1 to the channel estimation unit
1241, inputs the RS#2 to the channel estimation unit 1242, and
inputs the data channel(s) to the signal separation/demodulation unit
126. The channel estimation unit 1241 performs channel estimation
based on the RS#1 and inputs the result of channel estimation to the
signal separation/demodulation unit 126. The channel estimation unit
1242 performs channel estimation based on the RS#2 and inputs the
result of channel estimation to the signal separation/demodulation unit
126. The signal separation/demodulation unit 126 separates the data
channel(s) into data channels transmitted from the respective antennas,
demodulates the data channels based on the corresponding results of
channel estimation, and inputs the demodulated data channels to the
switching unit 128.

[0088]When the data channel(s) is transmitted using four antennas from the
base station 200, the fast-Fourier-transformed signal is input to the
demultiplexing unit 122 (3). The demultiplexing unit 122 separates the
input signal into reference signals (RS) #1, #2, #3, and #4 and the data
channel(s), inputs the RS #1 to the channel estimation unit 1241,
inputs the RS#2 to the channel estimation unit 1242, inputs the RS#3
to the channel estimation unit 1243, inputs the RS#4 to the channel
estimation unit 1244, and inputs the data channel(s) to the signal
separation/demodulation unit 126.

[0089]The channel estimation unit 1241 performs channel estimation
based on the RS#1 and inputs the result of channel estimation to the
signal separation/demodulation unit 126. The channel estimation unit
1242 performs channel estimation based on the RS#2 and inputs the
result of channel estimation to the signal separation/demodulation unit
126. The channel estimation unit 1243 performs channel estimation
based on the RS#3 and inputs the result of channel estimation to the
signal separation/demodulation unit 126. The channel estimation unit
1244 performs channel estimation based on the RS#4 and inputs the
result of channel estimation to the signal separation/demodulation unit
126. The signal separation/demodulation unit 126 separates the data
channel(s) into data channels transmitted from the respective antennas,
demodulates the data channels based on the corresponding results of
channel estimation, and inputs the demodulated data channels to the
switching unit 128.

[0090]The switching unit 128, according to the selection result input from
the switching unit 120, outputs the data channel demodulated by the
one-antenna demodulation process, the data channels of the respective two
antennas demodulated by the two-antenna demodulation process, or the data
channels of the respective four antennas demodulated by the four-antenna
demodulation process.

[0091]The above embodiment eliminates the need for a user device to try
multiple demodulation patterns corresponding to different numbers of used
antennas and thereby makes it possible to simplify a reception process.

[0092]The descriptions and drawings in the above embodiments should not be
construed to be limiting the present invention. A person skilled in the
art may think of variations of the above embodiments from the
descriptions.

[0093]In other words, the present invention may also include various
embodiments not disclosed above. Therefore, the technical scope of the
present invention should be determined based on proper understanding of
the claims with reference to the above descriptions.

[0094]Although the present invention is described above in different
embodiments, the distinctions between the embodiments are not essential
for the present invention, and the embodiments may be used individually
or in combination. Although specific values are used in the above
descriptions to facilitate the understanding of the present invention,
the values are just examples and different values may also be used unless
otherwise mentioned.

[0095]The present invention is not limited to the specifically disclosed
embodiments, and variations and modifications may be made without
departing from the scope of the present invention. Although functional
block diagrams are used to describe apparatuses in the above embodiments,
the apparatuses may be implemented by hardware, software, or a
combination of them.

[0096]The present international application claims priority from Japanese
Patent Application No. 2007-026184 filed on Feb. 5, 2007, the entire
contents of which are hereby incorporated herein by reference.